Biofuels are of increasing interest for a number of reasons including: (1) they are a renewable resource, (2) their production is less dependent on geopolitical considerations, (3) they provide the possibility of a direct replacement of petroleum-based fuels in existing vehicles, and (4) the net greenhouse gas emissions can be substantially reduced by virtue of CO2 uptake by biofuel precursors—particularly in the case of cellulosic feedstocks.
An easily-obtainable biofuel is vegetable oil, which largely comprises glycerides and some free fatty acids. The properties of vegetable oil, however, make it generally inappropriate for use as a direct replacement for petroleum diesel in vehicle engines. The vegetable oils' viscosities are generally too high and they do not burn cleanly enough, thereby leaving damaging carbon deposits on the engine. Additionally, vegetable oils tend to gel, especially at low temperatures, thereby hindering their use in colder climates. These problems are mitigated when the vegetable oils are blended with petroleum fuels, but still remain an impediment for long-term use in diesel engines.
Hydroisomerization is often used to improve the low temperature properties of vegetable oils blended with petroleum fuels. But requiring a hydroisomerization process step for making blends that meet specifications adds significant cost. It is desirable to develop a process for making renewable transportation fuels that contain vegetable oils without the need for a hydroisomerization process step.
The foregoing has outlined rather broadly features of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.